1. Field of the Invention
This invention relates to a white balance device for a video camera.
2. Description of the Related Art
Many white balance devices for video camera as in the recent years in which the video camera has become smaller in size and lighter in weight and has become popular even to home use, have been proposed for automatic adjustment of the white balance. With this automatic white balance device, the photographer, when correcting the white balance, needs only to do a simple manipulation, or no manipulation at all. From these proposals, particular mention may be made of the technique called "automatic follow-up type" that is to employ the color signal either separated from the image signal of the video camera, or produced from the color temperature sensor which is positioned outside the image pickup system to detect the color temperature of the ambient illumination on the object to be photographed in order to carry out at all times the adjustment of the white balance. Hence, the photographer is freed from the consciousness of adjusting the white balance, since the white balance is always maintained correct automatically. Thus, the automatic follow-up type white balance device is very advantageous in handling the video camera.
Such a white balance device of the type described above has, however, a problem in that, when the image is sweeping fast on the pickup device, or when the photographer, by his intention on the composition, is turning the camera vertically or horizontally (panning) or tilting it, the ratio of the color components of the above-described color signal is caused to change, so that the color of the image is also changed, being unpleasant to view. To compensate for this defect, there has been another previous proposal that the above-described color signal is processed through an electrical circuit of comparatively large time constant (for instance, about several tens of seconds), before it is used for adjustment of the white balance. The use of this technique, however, produces an alternative problem in that, because, as the electrical power source is applied, or the conditions of the camera are largely changed, for example, the lens is capped, it takes a long time to stabilize the adjusting operation, the manageability is very lowered.